In an absorbent article such as a disposable diaper, in order to improve the fitting for the wearer, a structure containing gathers formed from elastic threads of Lycra (registered trademark) having elasticity in the waistline portion and the leg holes is adopted widely.
A process of manufacturing an absorbent article containing such gathers uses an elastic thread supply device for continuously supplying an elastic thread to a processing line in which the elastic thread is bonded on a web having a continuous nonwoven fabric, for example, (for example, Patent Literature 1). In such an elastic thread supply device, the so-called overend unwinding, in which the elastic thread is drawn sequentially in the axial core direction of a cylindrical elastic thread package around which the elastic thread is wound, is performed.
In the case of overend unwinding, because the elastic thread package does not rotate, the lead portion of a spare elastic thread package can be connected to the end portion of the elastic thread package in use. Therefore, even when one elastic thread package is used up, the processing line need not be stopped to change the elastic thread package.
On the other hand, when drawing the elastic thread by overend unwinding, a different action from that for a non-elastic thread is required. Specifically, as compared to a non-elastic thread, it is difficult to unwind an elastic thread smoothly, and the stress acting upon the elastic thread changes successively. Furthermore, a characteristic of an elastic thread is that it is stretched easily by a small amount of stress. Therefore, if an elastic thread drawn by overend unwinding is supplied as is to the processing line, then when the elastic thread is stretched in the processing line, a variation occurs in the stress acting upon the elastic thread, which might lead to a quality defect of the absorbent article.
Thus, an elastic thread supply device equipped with a tension controller to control the tension of the elastic thread drawn by overend unwinding is known (for example, Patent Literature 2). According to such an elastic thread supply device, because an elastic thread is supplied to the processing line after controlling the stress acting upon the elastic thread within a certain range by the tension controller, the quality defect of the absorbent article can be inhibited.